add clients_room in server.py and client_in_room in base_manager.py to get the number of clients in a room

src/socketio/base_manager.py

@@ -154,6 +154,13 @@ class BaseManager(object):
             pass
         return r
 
+    def client_in_room(self, room_in, namespace):
+        """Return the number of client in room"""
+        try:
+            return len(self.rooms[namespace][room_in])
+        except KeyError:
+            pass
+
     def emit(self, event, data, namespace, room=None, skip_sid=None,
              callback=None, **kwargs):
         """Emit a message to a single client, a room, or all the clients

src/socketio/server.py

@@ -472,6 +472,16 @@ class Server(object):
         namespace = namespace or '/'
         return self.manager.get_rooms(sid, namespace)
 
+    def clients_room(self, room, namespace=None):
+        """Return the number of clients in a room.
+
+        :param room: room selected.
+        :param namespace: The Socket.IO namespace for the event. If this
+                          argument is omitted the default namespace is used.
+        """
+        namespace = namespace or '/'
+        return self.manager.client_in_room(room, namespace)
+
     def get_session(self, sid, namespace=None):
         """Return the user session for a client.